1. Technical Field
This invention relates to transistors and, more particularly, to transistors fabricated using both focused ion beam and molecular beam epitaxy techniques to provide multiple functions from a single transistor.
2. Discussion
The number of functions an integrated circuit (IC) can perform is limited by the size of the IC. If each IC performs relatively few functions, several ICs must be used to provide the desired functionality, thus increasing system cost. The number of functions an IC can perform can be expressed as a ratio of the number of transistors per IC over the number of transistors per function. The number of transistors per IC is limited by the IC's scale of integration and power dissipation. For example, present day bipolar ICs are limited to 50,000 transistors. The number of transistors per IC can be increased by fabricating smaller transistor feature sizes, requiring very high capital investment. The number of transistors per function is limited by circuit design architecture and can be reduced by using fewer transistors per function which requires clever circuit design. For example a current mode logic (CML) bipolar half adder typically requires 26 transistors.
Conventional resonant tunneling diodes (RTDs) have been employed in multi-valued logic, multi-state memory, and analog-to-digital circuit applications. Conventional resonant tunneling transistors (RTTs) have been employed in digital integrated circuits and have high isolation and gain.
In addition to RTDs and RTTs, conventional resonant tunneling hot electron transistors (RHETs) have a high cutoff frequency (e.g. 120 GHz). A full adder has been fabricated using only seven RHETs and has a 40 ps delay time and 20 mW power consumption.
While the above-identified devices have decreased IC size and power consumption and increased IC speed, it is desirable to increase the number of functions per IC by reducing the number of transistors per function to further decrease size and power consumption and further increase IC speed.